The first thing I would suggest you do is get your partition information that is current so you know which partitions you have windows 7 on. If it is an OEM you may have a separate boot partition as well as a recovery partition. Make a note of this running: sudo fdisk -l command.
windows 7 will overwrite the Grub entry in the master boot record without informing you and AFAIK, there is nothing to be done about this. You can reinstall Grub after re-installing windows.
Generally in the above circumstances, you would put an entry in the grub menu.lst or grub.cfg file for windows after the install. If you are using Ubuntu Lucid you will have Grub 2. Haven't used it so all I can do is refer you to this tutorial on Grub 2: